A coating film consisting of a polyimide resin, which combines excellent heat resistance and electrical and mechanical characteristics, has been conventionally used in, for example, insulating materials for electronic parts and passivation films, surface protective films, and interlayer insulating films for semiconductor devices.
In forming the polyimide resin coating film, a non-photosensitive polyimide resin precursor composition or a photosensitive polyimide resin precursor composition can be used. What is provided in the form of the latter can be applied onto a substrate, followed by light exposure, development, and thermal imidation treatment, to more readily form a cured relief pattern resistant to heat. Thus, the polyimide resin precursor composition may be non-photosensitive or photosensitive when the polyimide resin is used as a coating film not required to form a relief pattern, but, in producing a semiconductor device having a cured relief pattern made of the polyimide resin, use of the photosensitive polyimide resin precursor composition enables the significant shortening of the process of the production thereof compared to that of the conventional non-photosensitive polyimide resin precursor composition.
However, when the above-described photosensitive polyimide resin precursor composition is used, it is necessary to employ a large amount of organic solvent such as a pyrrolidone or a ketone as a developer in the process of the development thereof. Thus, there is a need for such a countermeasure that the organic solvent is removed in view of safety and increased recent concern over environmental issues. To that end, various heat-resistant photosensitive resin materials developable with a dilute alkali aqueous solution have been recently proposed as is the case with a photoresist in the field of the above-described materials
Among others, processes using a hydroxypolyamide soluble in an alkali aqueous solution, for example, a polybenzoxazole resin precursor, have received attention in recent years; for example, processes using, as a positive photosensitive material, a composition in which the above-described precursor is mixed with an optically active ingredient such as naphtoquinonediazide have been proposed (see e.g. JP-B-01-46862). A process using, as a negative photosensitive material, a composition in which a precursor where groups having photopolymerizable unsaturated double bonding are introduced into part of the hydroxyl groups of the above-described precursor is mixed with a compound having photopolymerizable unsaturated double bonding and a photopolymerization initiator has been also proposed (see JP-A-2002-12665).
These processes facilitate the formation of relief patterns after development and make favorable the preservation stability of such compositions. In addition, since a cured relief pattern made of a polybenzoxazole resin has a heat resistance comparable to that of a cured relief pattern made of a polyimide resin, the polybenzoxazole resin precursor has received attention as a promising alternative material for an organic solvent-developable polyimide resin precursor.
Meanwhile, there have been marked changes in methods for packaging semiconductor devices in which the above-described materials are used. In place of a conventional LOC package in which a lead frames is jointed to a semiconductor device through a gold wire, there has tended to be used, in recent years, a package which adopts multilayer wiring in view of an improvement in integration density and function and the miniaturization of a chip. Thus, conditions to which a polyimide resin coating film or a polybenzoxazole resin coating film is exposed during the formation of the structure vary more than before, which requires greater chemical resistance e.g. to a photoresist peeling solution composed of a strong acid, strong base, or organic solvent such as dimethyl sulfoxide, a basic organic compound such as ethanolamine or tetramethylammonium hydroxide, and the like.
For a similar reason, a method for mounting a semiconductor device on a printed wiring board is being also changed from a conventional method using a metal pin and a lead-tin eutectic solder into a method using, with a view towards a chip size package, a structure enabling higher-density mounting such as BGA (ball grid array) in which a polyimide resin coating film or a polybenzoxazole resin coating film is directly contacted with a solder bump.
In other words, the polyimide resin coating film and the polybenzoxazole resin coating film have become required Lo have increased resistance to heat and to flux because there occurs a state where they contact the flux e.g. in the reflow process of the solder bump.
The polybenzoxazole resin coating film is generally prepared by subjecting a bisaminophenol compound and a dicarboxylic acid compound to polycondensation to produce a polybenzoxazole resin precursor which is then dissolved in an organic solvent to make a varnish-like composition, followed by forming a coating film e.g. through coating before further heating to high temperature to convert to a polybenzoxazole resin.
Specific examples of proposed polybenzoxazole resins designed to satisfy heat resistance, chemical resistance, and high-temperature flux resistance include polybenzoxazole resins obtained by heat curing polybenzoxazole resin precursors synthesized from 4,4′-diamino-3,3′-dihydroxybiphenyl and terephthalic acid, from 4,4′-diamino-3,3′-dihydroxybiphenyl and 4,4′-biphenyldicarboxylic acid, from 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane and terephthalic acid, and from 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane and 4,4′-biphenyldicarboxylic acid.
A dicarboxylic acid such as terephthalic acid or 4,4′-biphenyldicarboxylic acid can be used as described above to make the polybenzoxazole resin in the form of a polymer having a rigid skeleton to improve the heat resistance thereof. Meanwhile, however, when made in the form of a resin composition having positive photosensitivity by adding an optically active compound such as naphthoquinoneazide, the above-described polybenzoxazole resin precursor having a rigid skeleton has problems that it per se becomes less soluble in an alkali aqueous solution and that it makes difficult the process of lithography using an i-beam stepper because the transmission of the i-beam, an outgoing light from a mercury lamp, is significantly reduced. There is also a problem that the reduced solubility thereof in an organic solvent makes it difficult to produce the photosensitive resin composition itself (see JP-A-2003-105086).
In contrast, a polybenzoxazole resin precursor using 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane and isophthalic acid or diphenyl ether dicarboxylic acid is excellent in i-beam transmission and easy to process into various shapes because it is highly soluble in an organic solvent. However, a polybenzoxazole resin obtained by curing the precursor has a problem that the heat resistance, chemical resistance, and flux resistance thereof are lower than those of the above-described polybenzoxazole resin having a rigid skeleton (see JP-A-2003-105086).
JP-A-05-27245 discloses a composition containing a polyamide resin obtained by using an acid component of a specified structure such as 5-hydroxyisophthalic acid dodecanoate chloride and an acid component of a specified structure such as terephthalic acid in a certain molar ratio to react a diamine component such as diaminodiphenyl ether therewith. However, the composition disclosed in the document has been developed for use in a liquid crystal alignment layer per se, and has not been intended to be developed as a precursor of heat resistant resin excellent not only in solubility in an organic solvent but also in chemical resistance.
Then, there is a need for a polybenzoxazole resin precursor having increased solubility in an organic solvent wherein the heat curing thereof provide a polybenzoxazole resin which satisfies heat resistance, chemical resistance, and flux resistance at a high level.    Patent Document 1: JP-B-01-46862    Patent Document 2: JP-A-2002-12665    Patent Document 3: JP-A-2003-105086    Patent Document 4: JP-A-05-27245